Ultrastructural characteristics of ostrich eggshell: outer shell membrane and the calcified layers.

P.D.G Richards,P.A Richards,M.E Lee

doi:10.4102/jsava.v71i2.687

P.D.G Richards, P.A Richards + Show 1 more

Open Access

https://doi.org/10.4102/jsava.v71i2.687

Copy DOI

Abstract

The ultrastructure of the eggshell of the domestic hen has been well researched and structural studies of other avian species, such as the ostrich, often base their interpretation of egg shell structure on that of the chicken. In the ostrich, lowered hatchability and hatching trauma may be due to shell ultrastructural abnormalities. In the present study the ultrastructure of the calcified portion, and the outer shell membrane (OSM), of domesticated ostrich eggshells was investigated using standard electron microscopic techniques. Transmission and scanning electron microscopy studies demonstrated intimate contact between cup-shaped structures present on the OSM and the mammillary layer of the calcified portion of the shell. The initial calcium carbonate growth of the calcified shell was of a dendritic nature with nucleation sites on the surface of the cup's contents. The dendritic growth gave way to a more randomly-orientated, smaller crystallite growth structure, which changed in form as it neared the vertical crystal layer (VCL). The VCL is described as being both amorphous and 'crumbly' depending on the plane of fracture. These observations suggest that firstly, initial calcification is contained within the cups and is then directed outwards to form the shell and that secondly, the VCL may contain an evolutionary, calcified cuticular layer. These observations serve as a baseline for studies investigating the effect of shell structure and strength on hatchling trauma and the influence of maternal diet.

Highlights

The ultrastructure of the eggshell of the domestic hen (Gallus gallus domesticus) is well described[6,17,30]
Calcification of the egg is thought to start in the isthmus of the reproductive tract[12], where calcium deposition begins around organic nodules that are randomly distributed on the outer shell membrane[27]
Outer shell membrane The outer shell membrane (OSM) is composed of a number of layers of fibrous material

Summary

Introduction

The ultrastructure of the eggshell of the domestic hen (Gallus gallus domesticus) is well described[6,17,30]. As commercial interests are invested in egg quality, the relationship of the structure of the shell and egg quality has been investigated using various microscopy techniques[6,9]. Such studies have used fracture techniques to demonstrate the presence of between 5 and 6 layers associated with the eggshell, which tend to be remarkably constant across most avian species[5]. The ultimate strength of the eggshell of the chicken is thought to be determined by both the bird’s calcium ration during the initial hours of calcification and by the number of nucleation sites present on the outer shell membrane[12]. It is unlikely that the architecture of the shell’s outer membrane plays any decisive role in the inherent strength of the shell[12]

Methods

Results

Conclusion